import type { TerminalSession, Workspace } from "../../domain/models";
import { collectSessionIds, pruneWorkspaceNode } from "../../domain/workspace";

export type DetachSessionFromWorkspaceStateResult = {
  changed: boolean;
  sessions: TerminalSession[];
  workspaces: Workspace[];
  activeTabId?: string;
  dissolvedWorkspaceId?: string;
  replacementTabIds?: string[];
};

export type CloseSessionWorkspaceLayoutResult = {
  workspaces: Workspace[];
  removedWorkspaceId?: string;
  dissolvedWorkspaceId?: string;
  lastRemainingSessionId?: string;
};

export type CloseSessionsStateResult = {
  sessions: TerminalSession[];
  workspaces: Workspace[];
  tabOrder: string[];
  activeTabId?: string;
};

type DetachSessionFromWorkspaceStateOptions = {
  sessions: TerminalSession[];
  workspaces: Workspace[];
  sessionId: string;
};

export function replaceDissolvedWorkspaceTabOrder(
  tabOrder: readonly string[],
  workspaceId: string | undefined,
  replacementTabIds: readonly string[] | undefined,
): string[] {
  if (!workspaceId || !replacementTabIds?.length) return [...tabOrder];

  const uniqueReplacementIds = replacementTabIds.filter((tabId, index, list) => (
    tabId && list.indexOf(tabId) === index
  ));
  if (uniqueReplacementIds.length === 0) return [...tabOrder];

  if (!tabOrder.includes(workspaceId)) {
    const hasAllReplacementIds = uniqueReplacementIds.every((tabId) => tabOrder.includes(tabId));
    return hasAllReplacementIds ? [...tabOrder] : [
      ...tabOrder,
      ...uniqueReplacementIds.filter((tabId) => !tabOrder.includes(tabId)),
    ];
  }

  const replacementIdSet = new Set(uniqueReplacementIds);
  let inserted = false;
  const nextOrder: string[] = [];

  for (const tabId of tabOrder) {
    if (tabId === workspaceId) {
      if (!inserted) {
        nextOrder.push(...uniqueReplacementIds);
        inserted = true;
      }
      continue;
    }
    if (!replacementIdSet.has(tabId)) {
      nextOrder.push(tabId);
    }
  }

  return nextOrder;
}

export function closeSessionWorkspaceLayoutState(
  workspaces: readonly Workspace[],
  workspaceId: string | undefined,
  sessionId: string,
): CloseSessionWorkspaceLayoutResult {
  if (!workspaceId) return { workspaces: [...workspaces] };

  let removedWorkspaceId: string | undefined;
  let dissolvedWorkspaceId: string | undefined;
  let lastRemainingSessionId: string | undefined;
  const nextWorkspaces = workspaces
    .map((workspace) => {
      if (workspace.id !== workspaceId) return workspace;
      const prunedRoot = pruneWorkspaceNode(workspace.root, sessionId);
      if (!prunedRoot) {
        removedWorkspaceId = workspace.id;
        return null;
      }

      const remainingSessionIds = collectSessionIds(prunedRoot);
      if (remainingSessionIds.length === 1) {
        dissolvedWorkspaceId = workspace.id;
        lastRemainingSessionId = remainingSessionIds[0];
        return null;
      }

      // Closing the focused session must hand focus to a remaining one, or a
      // focus-mode workspace is left with a dangling focusedSessionId: no pane
      // qualifies as visible and the continuously rendered hidden panes all
      // paint on top of each other (#3046).
      const nextFocusedSessionId =
        workspace.focusedSessionId && !remainingSessionIds.includes(workspace.focusedSessionId)
          ? remainingSessionIds[0]
          : workspace.focusedSessionId;
      const nextFocusSessionOrder = workspace.focusSessionOrder?.filter(
        (candidateId) => remainingSessionIds.includes(candidateId),
      );

      return {
        ...workspace,
        root: prunedRoot,
        focusedSessionId: nextFocusedSessionId,
        focusSessionOrder: nextFocusSessionOrder,
      };
    })
    .filter((workspace): workspace is Workspace => Boolean(workspace));

  return {
    workspaces: nextWorkspaces,
    removedWorkspaceId,
    dissolvedWorkspaceId,
    lastRemainingSessionId,
  };
}

/**
 * Apply a close-session action to the session list using the layout result.
 * When a 2-pane workspace dissolves to one terminal, that remaining session
 * must become an orphan tab — not stay bound to a deleted workspaceId.
 */
export function applyCloseSessionToSessions(
  sessions: readonly TerminalSession[],
  sessionId: string,
  layoutResult: Pick<CloseSessionWorkspaceLayoutResult, "lastRemainingSessionId">,
): TerminalSession[] {
  const remaining = sessions.filter((session) => session.id !== sessionId);
  const lastRemainingSessionId = layoutResult.lastRemainingSessionId;
  if (!lastRemainingSessionId) return remaining;

  return remaining.map((session) => (
    session.id === lastRemainingSessionId
      ? { ...session, workspaceId: undefined }
      : session
  ));
}

export function isPreferredTabAvailableAfterClose(
  input: {
    preferredTabId: string | null | undefined;
    closedSessionId: string;
    layoutResult: CloseSessionWorkspaceLayoutResult;
    remainingSessions: readonly TerminalSession[];
  },
): input is {
  preferredTabId: string;
  closedSessionId: string;
  layoutResult: CloseSessionWorkspaceLayoutResult;
  remainingSessions: readonly TerminalSession[];
} {
  const { preferredTabId, closedSessionId, layoutResult, remainingSessions } = input;
  if (!preferredTabId || preferredTabId === closedSessionId) return false;
  if (
    preferredTabId === layoutResult.dissolvedWorkspaceId
    || preferredTabId === layoutResult.removedWorkspaceId
  ) {
    return false;
  }
  if (preferredTabId === "vault" || preferredTabId === "sftp") return true;
  if (layoutResult.workspaces.some((workspace) => workspace.id === preferredTabId)) return true;
  return remainingSessions.some((session) => (
    session.id === preferredTabId
    && !session.workspaceId
    && !session.hiddenFromTabs
  ));
}

export function resolveActiveTabAfterCloseSession({
  currentActiveTabId,
  closedSessionId,
  workspaceId,
  layoutResult,
  remainingSessions,
  preferredTabId,
}: {
  currentActiveTabId: string | null;
  closedSessionId: string;
  workspaceId: string | undefined;
  layoutResult: CloseSessionWorkspaceLayoutResult;
  remainingSessions: readonly TerminalSession[];
  preferredTabId?: string | null;
}): string | null {
  const fallbackWorkspace = layoutResult.workspaces[layoutResult.workspaces.length - 1];
  const fallbackSolo = remainingSessions.filter((session) => !session.workspaceId && !session.hiddenFromTabs).slice(-1)[0];
  const preferredInput = {
    preferredTabId,
    closedSessionId,
    layoutResult,
    remainingSessions,
  };
  const preferredFallback = isPreferredTabAvailableAfterClose(preferredInput)
    ? preferredInput.preferredTabId
    : undefined;
  const fallback = layoutResult.lastRemainingSessionId
    ?? preferredFallback
    ?? fallbackWorkspace?.id
    ?? fallbackSolo?.id
    ?? "vault";

  if (
    currentActiveTabId === closedSessionId
    || (layoutResult.dissolvedWorkspaceId && currentActiveTabId === layoutResult.dissolvedWorkspaceId)
    || (layoutResult.removedWorkspaceId && currentActiveTabId === layoutResult.removedWorkspaceId)
    || (workspaceId && currentActiveTabId === workspaceId && !layoutResult.workspaces.some((ws) => ws.id === workspaceId))
  ) {
    return fallback;
  }

  return null;
}

export function closeSessionsState({
  sessions,
  workspaces,
  sessionIds,
  currentActiveTabId,
  preferredTabId,
  tabOrder,
}: {
  sessions: readonly TerminalSession[];
  workspaces: readonly Workspace[];
  sessionIds: readonly string[];
  currentActiveTabId: string | null;
  preferredTabId?: string | null;
  tabOrder: readonly string[];
}): CloseSessionsStateResult {
  let nextSessions = [...sessions];
  let nextWorkspaces = [...workspaces];
  let nextTabOrder = [...tabOrder];
  let nextActiveTabId = currentActiveTabId;
  let resolvedActiveTabId: string | undefined;

  for (const sessionId of new Set(sessionIds)) {
    const targetSession = nextSessions.find((session) => session.id === sessionId);
    if (!targetSession) continue;

    const workspaceId = targetSession.workspaceId;
    const layoutResult = closeSessionWorkspaceLayoutState(
      nextWorkspaces,
      workspaceId,
      sessionId,
    );
    nextWorkspaces = layoutResult.workspaces;
    nextSessions = applyCloseSessionToSessions(nextSessions, sessionId, layoutResult);

    if (layoutResult.dissolvedWorkspaceId && layoutResult.lastRemainingSessionId) {
      nextTabOrder = replaceDissolvedWorkspaceTabOrder(
        nextTabOrder,
        layoutResult.dissolvedWorkspaceId,
        [layoutResult.lastRemainingSessionId],
      );
    }

    const activeTabAfterClose = resolveActiveTabAfterCloseSession({
      currentActiveTabId: nextActiveTabId,
      closedSessionId: sessionId,
      workspaceId,
      layoutResult,
      remainingSessions: nextSessions,
      preferredTabId,
    });
    if (activeTabAfterClose) {
      nextActiveTabId = activeTabAfterClose;
      resolvedActiveTabId = activeTabAfterClose;
    }
  }

  return {
    sessions: nextSessions,
    workspaces: nextWorkspaces,
    tabOrder: nextTabOrder,
    activeTabId: resolvedActiveTabId,
  };
}

export function detachSessionFromWorkspaceState({
  sessions,
  workspaces,
  sessionId,
}: DetachSessionFromWorkspaceStateOptions): DetachSessionFromWorkspaceStateResult {
  const session = sessions.find((candidate) => candidate.id === sessionId);
  if (!session?.workspaceId) {
    return { changed: false, sessions, workspaces };
  }

  const workspaceId = session.workspaceId;
  const targetWorkspace = workspaces.find((workspace) => workspace.id === workspaceId);
  if (!targetWorkspace) {
    return { changed: false, sessions, workspaces };
  }

  const prunedRoot = pruneWorkspaceNode(targetWorkspace.root, sessionId);
  let nextSessions = sessions.map((candidate) => (
    candidate.id === sessionId ? { ...candidate, workspaceId: undefined } : candidate
  ));

  if (!prunedRoot) {
    return {
      changed: true,
      sessions: nextSessions,
      workspaces: workspaces.filter((workspace) => workspace.id !== workspaceId),
      activeTabId: sessionId,
      dissolvedWorkspaceId: workspaceId,
      replacementTabIds: [sessionId],
    };
  }

  const remainingSessionIds = collectSessionIds(prunedRoot);
  if (remainingSessionIds.length === 1) {
    nextSessions = nextSessions.map((candidate) => (
      candidate.id === remainingSessionIds[0] ? { ...candidate, workspaceId: undefined } : candidate
    ));

    return {
      changed: true,
      sessions: nextSessions,
      workspaces: workspaces.filter((workspace) => workspace.id !== workspaceId),
      activeTabId: sessionId,
      dissolvedWorkspaceId: workspaceId,
      replacementTabIds: [sessionId, ...remainingSessionIds],
    };
  }

  const nextFocusedSessionId = remainingSessionIds.includes(targetWorkspace.focusedSessionId)
    ? targetWorkspace.focusedSessionId
    : remainingSessionIds[0];
  const nextFocusSessionOrder = (targetWorkspace.focusSessionOrder ?? [])
    .filter((candidateId, index, list) => (
      candidateId !== sessionId &&
      remainingSessionIds.includes(candidateId) &&
      list.indexOf(candidateId) === index
    ));
  for (const remainingSessionId of remainingSessionIds) {
    if (!nextFocusSessionOrder.includes(remainingSessionId)) {
      nextFocusSessionOrder.push(remainingSessionId);
    }
  }

  return {
    changed: true,
    sessions: nextSessions,
    workspaces: workspaces.map((workspace) => (
      workspace.id === workspaceId
        ? {
            ...workspace,
            root: prunedRoot,
            focusedSessionId: nextFocusedSessionId,
            focusSessionOrder: nextFocusSessionOrder,
          }
        : workspace
    )),
    activeTabId: sessionId,
  };
}